Growing demand for integrated circuits (ICs), for example microprocessors, with ever higher levels of performance and functionality have driven these devices to circuit densities beyond 100 million transistors per die. This number may soon exceed one billion transistors on a single die. The growth in transistor density has been made possible by the use of MOSFET transistors with gate lengths below 100 nm. As gate length has shortened, power supply voltages have fallen, in some cases, to below 1 V.
High-speed microprocessors, with clock speeds above 3 GHz, may require in excess of 100 watts of power when operating at maximum load. With operating voltages below 1 V, this translates to power supply currents that reach beyond 100 A. Additionally, the current requirements may change from idle (<20 A) to full power in a small number of clock cycles, leading to current transitions (di/dt) exceeding 30 GA/s.
Integrated circuits are typically powered from one or more DC supply voltages provided by external supplies and converters. The power is provided through pins, leads, lands, or bumps on the integrated circuit package. The traditional method for providing such high power to integrated circuits may involve the use of a high-efficiency, programmable DC-to-DC (switch-mode) power converter located near the IC package. This type of converter (buck regulator) may use a DC input voltage as high as 48 V and provide a DC output voltage below 2 V. Conventional DC-to-DC power converters use switching frequencies in the neighborhood of 200 KHz, with some high-end units in the 1-2 MHz range. Such converters usually require a handful of relatively large components, including a pulse-width modulation (PWM) controller, one or more power transistors, filter and decoupling capacitors, and one or more large inductors and/or transformers. These components are costly and require significant space on the printed circuit board in the neighborhood of the integrated circuit.
Another problem with having to provide currents in excess of 100 A and a di/dt above 30 GA/s to an integrated circuit is the need to use a significant number of input/output (I/O) pins on the integrated circuit package to feed power to the chip. For example, a 3.8 GHz Intel® Pentium® 4 microprocessor (from Intel Corporation of Santa Clara, Calif.) in a 775-land Land Grid Array package uses 226 power lands (VCC) and 273 ground lands (VSS) to support a maximum current of 119 A. This amounts to nearly ⅔ of all of the I/O lands dedicated to feeding power to the processor core.